The present invention relates generally to electro-optical components, and specifically to electrical biasing of the components.
In order for an electro-optical component, such as an Electro-Absorption Modulator (EAM) or a photo-diode detector (PDD), to function correctly, the element typically requires the ability to be independently DC biased and AC modulated. In addition to these electrical requirements, the element usually also needs to be aligned optically.
FIG. 1 illustrates apparatus, known in the art, for electrically and optically coupling an electro-optical component 10. Component 10 is mounted on a first capacitor 24, which typically has a capacitance of the order of 1 nF, so that a lower electrode 17 of the component mates with a first electrode 19 of the capacitor. Capacitor 24 is in turn mounted on a conductive optical bench 26, so that a second electrode 11 of the capacitor is in electrical contact with the optical bench. A second capacitor 28, typically having a capacitance of the order of 1 xcexcF, is coupled in parallel with capacitor 24, the two capacitors forming a low impedance path for low and high AC frequencies between the optical bench and the optical element. Optical bench 26 is electrically connected to a ground conductor 12 of a transmission strip-line 16. A second conductor 14 of the transmission strip-line is bonded, by a wire 18, to an upper electrode 22 of component 10. Typically, a resistor 21 may be connected between electrode 22 and ground 12. The resistor serves as an impedance match and as a DC return.
Electro-optical component 10 is aligned with an optical element 20, such as a fiber optic, by adjusting optical element 20. When alignment is achieved, optical element 20 is mechanically coupled to the optical bench.
The arrangement of elements as shown in FIG. 1 provides DC isolation of electro-optical component 10 from ground conductor 12, while enabling the component to be modulated by an AC voltage via capacitors 24 and 28. Thus, electro-optical component 10 may be DC biased independent of any AC modulation provided to the element, by applying a DC bias level to electrode 17 and applying a ground potential to electrode 22 via resistor 21. However, this method of arranging elements in order to be able to DC bias electro-optical component 10 separates the component from optical bench 26, causing severe difficulties in aligning the component. An improved arrangement for aligning an electro-optical component is thus required.
It is an object of some aspects of the present invention to provide a method and apparatus for biasing and optically aligning an electro-optical component.
In preferred embodiments of the present invention, an electro-optical assembly comprises a transmission line which is coupled to an electro-optical component. The electro-optical component comprises a first and a second electrode coupled to an optical region, the optical region being aligned optically. The transmission line, preferably a micro-strip line, comprises a xe2x80x9clivexe2x80x9d conductor and a ground conductor, the ground conductor being divided into a first ground section and a second ground section by a non-conducting gap formed in the second conductor, so that the two ground sections are mutually isolated from a direct current (DC) point of view. The two ground sections are connected by one or more capacitors which effectively short-circuit the two sections from an alternating current (AC) point of view. The second ground section is bonded to a conductive optical bench, upon which the electro-optical component is positioned directly, the first electrode of the component being bonded to the optical bench. The second electrode of the electro-optical component is electrically connected to the live conductor of the micro-strip.
The assembly thus enables the electro-optical component to be DC biased independently of an AC level which feeds the component. Furthermore, since the electro-optical component mates directly with the optical bench, optical alignment of the component is significantly easier than electro-optical assemblies wherein the component is not in direct contact with the optical bench.
In some preferred embodiments of the present invention, the assembly is implemented as two sub-assemblies. A first sub-assembly comprises the transmission line implemented as described above and coupled with the one or more capacitors. A second sub-assembly comprises the electro-optical component mated with the optical bench. Preferably, the second sub-assembly is used to optically align the electro-optical component, and then the first sub-assembly is coupled to the second sub-assembly, to form the complete electro-optical assembly.
There is therefore provided, according to a preferred embodiment of the present invention, an electro-optical assembly, including:
an optical sub-assembly, including:
an electro-optical component including an optical region and a first and a second electrode coupled thereto; and
a conductive optical bench in contact with the second electrode of the electro-optical component, the optical bench being adapted to permit optical alignment of the electro-optical component while making such contact; and
a transmission line including:
a live conductor;
a ground conductor insulated from the live conductor; and
a port adapted to receive a signal, such that the live and ground conductors are coupled to the first and second electrodes of the electro-optical component so as to convey the signal between the port and the electro-optical component and to provide a direct current (DC) bias level to the electro-optical component independent of the signal.
Preferably, the conductive optical bench is in direct mechanical and electrical contact with the second electrode.
Preferably, the transmission line includes a micro-strip line which is adapted to operate at frequencies up to approximately 50 GHz.
Preferably, the ground conductor includes a first ground section and a second ground section separated from the first ground section by an insulating gap, wherein the first and second ground sections are coupled together capacitively, and wherein the first ground section is connected to the conductive optical bench.
Further preferably, the first and second ground sections are coupled by at least one capacitor so as to form an effective short-circuit between the two sections at alternating current (AC) frequencies in a range from approximately 1 kHz to approximately 50 GHz.
Further preferably, the transmission line and the at least one capacitor are fabricated as an electrical sub-assembly, and the electro-optical assembly is fabricated by coupling the electrical sub-assembly to the optical sub-assembly.
Preferably, the optical bench is adapted to permit the optical alignment after the live and ground conductors of the transmission line are coupled to the first and second electrodes of the electro-optical component.
Preferably, the assembly includes circuitry which matches an impedance of the electro-optical component to the impedance of the transmission line.
Further preferably, the circuitry includes a resistor connected between the first electrode and the ground conductor.
Alternatively or additionally, the circuitry includes a resistor and a capacitor connected in series between the first electrode and the conductive optical bench.
There is further provided, according to a preferred embodiment of the present invention, an electro-optical assembly, including:
an electro-optical component including an optical region and a first and a second electrode coupled thereto;
a conductive optical bench, in contact with the second electrode of the electro-optical component, the bench being adapted to permit optical alignment of the electro-optical component while making such contact;
a transmission line including a live conductor and a ground conductor insulated from the live conductor, the live conductor being bonded to the first electrode of the electro-optical element, the ground conductor including a first ground section and a second ground section electrically connected to the optical bench and insulated from the first ground section by a non-conductive gap therebetween, the second ground section being capacitively coupled to the first ground section.
Preferably, the conductive optical bench is in direct mechanical and electrical contact with the second electrode.
Preferably, the transmission line includes a micro-strip line which is adapted to operate at frequencies up to approximately 50 GHz.
Preferably, the first and second ground sections are coupled by at least one capacitor so as to form an effective short-circuit between the two sections at alternating current (AC) frequencies in a range from approximately 1 kHz to approximately 50 GHz.
Preferably, the optical bench is adapted to permit the optical alignment after the live and ground conductors of the transmission line are coupled to the first and second electrodes of the electro-optical component.
Preferably, the assembly includes circuitry which matches an impedance of the electro-optical component to the impedance of the transmission line.
Further preferably, the circuitry includes a resistor connected between the first electrode and the first ground section.
Alternatively or additionally, the circuitry includes a resistor and a capacitor connected in series between the first electrode and the conductive optical bench.
There is further provided, according to a preferred embodiment of the present invention, a method for operating an electro-optical assembly, including:
positioning an electro-optical component including an optical region and a first and a second electrode coupled thereto, so that the second electrode contacts a conductive optical bench;
aligning the electro-optical component while maintaining the contact; and
coupling a transmission line, including a live conductor and a ground conductor insulated from the live conductor and a port adapted to receive a signal, to the electro-optical component, such that the live and ground conductors are coupled to the first and second electrodes of the electro-optical component, the transmission line being adapted to convey the signal between the port and the electro-optical component and to enable a direct current (DC) bias level to be applied to the electro-optical component independent of the signal.
Preferably, positioning the electro-optical component includes placing the component in direct mechanical and electrical contact with the second electrode.
Preferably, the transmission line includes a micro-strip line which is adapted to operate at frequencies up to approximately 50 GHz.
Preferably, the ground conductor includes a first ground section and a second ground section separated from the first ground section by an insulating gap, and wherein coupling the transmission line includes coupling the first and second ground sections capacitively and connecting the first ground section to the conductive optical bench.
Further preferably, coupling the first and second ground sections capacitively includes coupling the first and second ground sections by at least one capacitor so as to form an effective short-circuit between the two sections at alternating current (AC) frequencies in a range from approximately 1 kHz to approximately 50 GHz.
Preferably, the method includes:
fabricating the transmission line and the at least one capacitor as an electrical sub-assembly;
fabricating the electro-optical component and the conductive optical bench as an optical sub-assembly; and
coupling the electrical sub-assembly to the optical sub-assembly to form the electro-optical assembly.
Preferably, aligning the electro-optical component includes performing an alignment after coupling the transmission line.
Preferably, aligning the electro-optical component includes adjusting an optical element to be in alignment with the electro-optical component and mechanically coupling the optical element to the conductive optical bench after performing the adjustment.
Preferably, the method includes matching an impedance of the electro-optical component to the impedance of the transmission line.
Further preferably, matching the impedance includes connecting a resistor between the first electrode and the ground conductor.
Alternatively or additionally, matching the impedance includes connecting a resistor and a capacitor in series between the first electrode and the conductive optical bench.
There is further provided, according to a preferred embodiment of the present invention, a method for operating an electro-optical assembly, including:
positioning an electro-optical component, having an optical region and a first and a second electrode coupled thereto, on a conductive optical bench so that the second electrode contacts the bench;
aligning the electro-optical component while the second electrode is in contact with the bench;
bonding a live conductor of a transmission line to the first electrode of the electro-optical component;
providing a first ground section of the transmission line for connection to a ground; and
connecting a second ground section of the transmission line, which is separated by a non-conductive gap from the first ground section and is capacitively coupled to the first ground section, to the optical bench.
Preferably, positioning the electro-optical component includes placing the conductive optical bench in direct mechanical and electrical contact with the second electrode.
Preferably, the transmission line includes a micro-strip line which is adapted to operate at frequencies up to approximately 50 GHz.
Preferably, the method includes coupling the first and second ground sections by at least one capacitor so as to form an effective short-circuit between the two sections at alternating current (AC) frequencies in a range from approximately 1 kHz to approximately 50 GHz.
Preferably, aligning the electro-optical component includes performing an alignment after bonding the live conductor of the transmission line and connecting the second ground section of the transmission line.
Preferably, aligning the electro-optical component includes adjusting an optical element to be in alignment with the electro-optical component and mechanically coupling the optical element to the conductive optical bench after performing the adjustment.
Preferably, the method includes matching an impedance of the electro-optical component to the impedance of the transmission line.
Further preferably, matching the impedance includes connecting a resistor between the first electrode and the first ground section.
Alternatively or additionally, matching the impedance includes connecting a resistor and a capacitor in series between the first electrode and the conductive optical bench.